Characterization of Ambient Aerosol Sources and Processes during CalNex 2010 with Aerosol Mass Spectrometry.

摘要

A suite of measurements from the CalNex Pasadena ground site are utilized to characterize aerosols, especially organic aerosols (OA), in the Los Angeles Basin. The concentrations of the species comprising PM2.5 and PM1 are quantified. Sea salt exhibits extensive chloride depletion due to chemical aging leading to substantial super micron nitrate. Five OA components are identified using positive matrix factorization including hydrocarbon-like organic aerosol (HOA), cooking-influenced organic aerosol (CIOA), and two types of oxygenated organic aerosol (OOA). The correlations with tracers and photochemical age indicate that HOA is a surrogate for primary combustion OA, and OOA is dominated by secondary OA (SOA) mass. A majority of the OA mass is OOA, with lesser contributions from HOA and CIOA. HOA concentrations are lower on Sundays displaying a weekly cycle consistent with reductions in diesel emissions. The OOA to odd-oxygen (ozone + NO2) rations for Pasadena, Mexico City, and Riverside are nearly equal, suggesting that SOA and odd-oxygen formation rates are proportional at the different sites. Dilution-corrected OA enhancements for Pasadena increase with photochemical age similar to or slightly higher that analogous data for Mexico City and the North Eastern United States. The OA elemental composition for Pasadena is described in a Van Krevelen diagram (H/C vs. O/C) and follows a common evolution. After propagation of uncertainties, a diesel contribution to SOA of 0-35% is a calculated based on the lack of an observed weekly cycle.